Miscible flooding process using improved soluble oil compositions



OR Lisa-829K532 3,482,632 MISCIBLE FLOODIN G PROCESS USING IM- PROVEDSOLUBLE OIL COMPOSITIONS LeRoy W. Holm, Fullerton, Calif., assignor toUnion Oil Company of California, Los Angeles, Calif., a corporation ofCalifornia No Drawing. Filed Mar. 15, 1968, Ser. No. 713,303 Int. Cl.E21]; 43/22 US. Cl. 166-273 19 Claims ABSTRACT OF THE DISCLOSURE Amiscible flooding process for the recovery of oil from subterraneanreservoirs in which an improved soluble oil composition comprising amixture of liquid hydrocarbon, a surface active agent and butylCellosolve is injected into the reservoir through an injection well, andthereafter an aqueous flooding agent is injected to drive the solubleoil composition towards a spaced production well. The soluble oilcomposition can be injected into the reservoir as a substantiallyanhydrous liquid or as a water-in-oil microemulsion.

This invention relates to the recovery of oil from subterraneanpetroleum reservoirs, and more particularly to an improved miscibleflooding process for the recovery of petroleum.

It has long been recognized that substantial amounts of oil remainunrecovered at the completion of normal primary recovery operations.Hence, various secondary methods of recovering additional quantities ofoil having been proposed, such as the well-known technique of waterflooding in which water is injected into the reservoir through aninjection well to drive additional oil toward one or more productionwells spaced apart in the reservoir from the injection well. Although anadditional quantity of oil can often be recovered by water flooding, theefficiency of the water flood and the ultimate oil recovery can befurther improved by introducing a solvent that is miscible with both theconnate oil and with the flood water into the reservoir aheadof theflood water.

One particular solvent system that has been suggested for use with awater drive comprises a mixture of substantially anhydrous soluble oiland an inert, nonaqueous solvent, preferably admixed in such proportionsthat the viscosity of the mixture approximates the viscosity of theformation oil. The soluble oil consists of a hydrocarbon phase; one ormore soaps or non-soap surface active materials; and a stabilizing agentwhich is usually a monohydric or polyhydric alcohol, or other partiallyoxygenated, low molecular weight hydrocarbon, such as a ketone. Thesoluble oil often contains some free organic acid, and especially afatty acid, such as oleic acid.

It has also been proposed that the flood water be preceded by amicroemulsion consisting of a soluble oil containing substantialquantities of water, such as from about to 50 percent or more water.These microemulsions are relatively stable, transparent emulsions of theWater-in-oil type, i.e., oil is the continuous phase and small dropletsof Water are dispersed therein.

While the foregoing anhydrous soluble oils and microemulsions areeffective in recovering more oil than recovered by conventional waterflooding, it is nevertheless desirable to even further improve themiscible flooding process to reduce its cost and to recover additionalamounts of oil.

Accordingly, a principal object of this invention is to provide animproved miscible flooding process for the recovery of petroleum fromsubterranean reservoirs. Another object of the invention is to provide amiscible warm! ilri l if 3,432,632 Patented Dec.9, i969 ice floodingprocess in which an improved miscible displacement fluid is injectedinto an oil-containing reservoir and thereafter driven through thereservoir by flood water. A further object of the invention is toprovide a miscible flooding process employing an improved soluble oilcomposition as the miscible displacement fluid. A still further objectof the invention is to provide a miscible flooding process utilizing animproved water-in-oil microemulsion as the miscible displacement fluid.Other objects and advantages of the invention will be apparent from thefollowing description.

Briefly, this invention contemplates a process for recovering oil fromsubterranean reservoirs in which an improved soluble oil compositioncomprising a mixture of liquid hydrocarbon, a surface active agent andbutyl Cellosolve is injected into the reservoir through an injectionwell, and thereafter an aqueous flooding agent is injected to drive themiscible displacement fluid towards a production well spaced apart inthe reservoir from the injection well. The soluble oil can be injectedinto the reservoir as an anhydrous liquid, or it can be injected as awater-in-oil microemulsion.

More specifically, this invention involves a miscible flooding processin which oil is displaced from a subterranean oil-bearing reservoir byan improved soluble oil composition containing a minor proportion ofbutyl Cellosolve. In the practice of the invention, a slug of theimproved soluble oil composition in the form of a substantiallyanhydrous liquid or a Water-in-oil microemulsion is injected into thereservoir through one or more injection or input wells penetrating theoil-bearing formation and forced through the reservoir by subsequentlyinjected flood water toward at least one production or output wellsimilarly completed in the reservoir. As the miscible flooding mediumpasses through the reservoir, it displaces residual oil therein andmoves it into the producing well whereupon the oil can be recovered byconventional means. The injection and productionwells can be arranged inany convenient pattern designed to achieve maximum contact of theoil-bearing zones by the advancing flood front, such as the conventionalfive-spot pattern wherein a central producing well is surrounded by foursomewhat symmetrically located injection Wells. Another of theconventional flooding patterns that can be employed in the practice ofthis invention is the line drive pattern in which the injection wellsare arranged in a line so that the injected flooding medium advancesthrough the formation to displace oil toward one or more spacedproduction wells that can also be arranged in a line substantiallyparallel to the line of injection wells.

The soluble oils used herein are oleaginous compositions which have theability to spontaneously emulsify With water when admixed therewith.These soluble oils comprise a liquid hydrocarbon, one or more selectedsurface active agents, and a minor proportion of butyl Cellosolve. Theemulsions formed by the addition of 'Water to a soluble oil are of thewater-in-oil type in that at water concentrations less than theinversion concentration, oil is the continuous phase and the water isdispersed in the oil in the form of very fine droplets, or micelles,which are less than about 0.1 micron in size, and usually range in sizefrom about to 600 A. These emulsions are generally transparent inappearance, and are stable in that they remain as microemulsions onaging. By transparent, it is meant that the microemulsions do not have acloudy or opaque appearance, even though they may contain color bodies.It is recognized, of course, that some cloudiness may appear at certainwater concentrations without adversely affecting the utility of the"microemulsions as a miscible displacement agent. Emulsions of this typeare designated microemulsions to distinguishthem from ordinarywater-in-oil macroemulsions in which the lower limit of particle size ofthe water droplets is about 0.1 micron. At water concentrations abovethe inversion concentration, the emulsion inverts to an emulsion of thewater-in-oil type in which droplets of oil are dispersed in a continuouswater phase. It is preferred that the water concentrations of themicroemulsion of this invention be maintained below the inversionconcentration so as to prevent inversion to emulsions of theoil-in-water type.

One of the major constituents of the improved soluble oil composition ofthis invention is a liquid hydrocarbon, which can comprise a crudepetroleum oil, such as a crude oil previously recovered from thereservoir, or other conveniently available crude oil; a refined or semirefined petroleum roduct, such as gasoline, naphtha, stove oil anddiesel; a residual product obtained by the distillation of lower boilingfractions from a crude oil, such as bunker fuel oil and other residualproducts; a low value refinery byproduct, such as catalytic cycle oil,lube oil extract, and the like; and liquefied normally gaseoushydrocarbons such as propane, butane and LPG.

While soluble oils can be prepared from any of these hydrocarbonmaterials, or mixtures of hydrocarbons, it has ben found that oilrecoveries are especially increased by miscible flooding with a solubleoil or microemulsion compounded with crude petroleum oil, or otherhydrocarbon mixture containing relatively high-boiling hydrocarbonconstituents, and butyl Cellosolve. By relatively high-boilinghydrocarbons is meant those boiling at least above about 400 F., andmore preferably above about 600 F. The hydrocarbon base stock cancontain lowboiling hydrocarbons boiling below about 400 F. withoutadversely affecting oil recovery, so long as a substantial portion ofthe base stock is comprised of the highboiling components. For example,excellent displacement efiiciencies are obtained with soluble oilscompounded from crude petroleum, even though the crude petroleumcontains some fractions boiling as low as 100 F. Thus, the miscibledisplacement fluids preferred for use in the practice of this inventioncomprise mixtures of crude petroleum or other hydrocarbon mixturescontaining relatively high-boiling hydrocarbon constituents, a surfaceactive agent, and butyl Cellosolve.

Surface active materials which can be used are those that when admixedwith the hydrocarbon cause the formation of microemulsions of thewater-in-oil type on the subsequent addition of water. Agents whichexhibit this property can be defined by their hydrophilic-lipophilicbalance and by their spreading coeflicients. The hydrophilic-lipophilicbalance is an indication of the size and strength of the hydrophilic, orwater-loving, or polar groups, and the lipophilic, oil-loving, ornon-polar, groups in a surfactant material expressed by a numericalvalue designated HLB number. The spreading coefficient is an indicationof the facility with which one liquid spreads upon another liquid.Spreading coeflicients greater than indicate that the first liquid willspread on the second, and coeflicients less than 0 indicate that thesupernatant liquid will simply form floating lenslike drops.Accordingly, surface active materials, or mixtures of materialspossessing the ability to spontaneously emulsify Water in oil exhibitaverage HLB numbers of about 3 to 7, and the most negative spreadingcoefficient consistent with the system.

A number of surface active materials that exhibit the ability tospontaneously emulsify oil and water to produce waterin-oilmicroemulsions are commercially available. Among the preferred agentsare various preferentially oilsoluble anionic surfactants such as thehigher alkyl aryl sulfonates, particularly the alkyl naphthenicmonosulfonates. A particularly preferred surface active agent is analkyl aryl monosulfonate prepared by sulfonation of an aromaticpetroleum fraction. These sulfonates are preferably in the form of theirsodium salts, however, other salts can be used.

4 Butyl Cellosolve is a colorless liquid solvent, miscible both withwater and with oil, and is chemically designated glycol monobutyl etheror 2-butoxyethanol. When included in a minor proportion in the solubleoil compositions of this invention, butyl Cellosolve functions as astabilizing agent rendering the surface active component of the solubleoil more effective and improving the stability of the resultingmicroemulsion. Further, it has been discovered that miscible floodingwith soluble oils and microemulsions containing a minor proportion ofbutyl Cellosolve results in the recovery of increased quantities of oil.While the exact mechanism by which the increased recovery is effected isnot understood, it has nevertheless been demonstrated that miscibleflooding with soluble oils and microemulsions containing butylCellosolve is more efficient than flooding with similar soluble oils andmicroemulsions containing other stabilizing agents, such as isopropylalcohol, particularly where the soluble oil or microemulsion iscompounded with a hydrocarbon containing relatively high-boilingconstituents.

A preferred composition in accordance with this invention useful as amiscible displacement fluid comprises a mixture of about 45 to 75percent liquid hydrocarbon, such as crude petroleum or other highboiling hydrocarbon; 8 to 30 percent of a surface active material, suchas an alkyl aryl monosulfonate obtained by sulfonation of an aromaticpetroleum fraction; 3 to 8 percent butyl Cellosolve; and 0 to 40 percentWater. Also, where the hydrocarbon liquid has a relatively highviscosity, light liquid hydrocarbon can be added to increase themobility of the resulting soluble oil to obtain a more favorablemobility ratio between the soluble oil and the following drive fluid.The light hydrocarbon will usually not constitute more than 25 volumepercent of the resulting soluble oil.

The compostiions useful in the practice of this invention can beprepared by any of the conventional techniques. One suitable method ofpreparing these compositions is to first admix the hydrocarbon basestock, surface active material and butyl Cellosolve in the desiredproportions to form a substantially anhydrous soluble oil. Thereafter,if desired, Water is added to obtain a microemulsion of the desiredWater content. Preferably, the water employed in forming themicroemulsion is a salt-containing fresh water having a dissolved saltcontent of less than about 5000 p.p.m.

The quantity of soluble oil or microemulsion injected should besuflicient to establish in the reservoir a miscible bank which can bedisplaced through the reservoir by the subsequently injected aqueousflooding medium. Satisfactory recoveries can usually be obtained by theinjection of 0.01 to 0.15 reservoir pore volume of the soluble oil ormicroemulsion.

In one preferred embodiment of this invention, a hydrocarbon, such aspreviously recovered reservoir oil; a mixed alkyl aryl monosulfonateobtained by sulfonation of an aromatic petroleum fraction; and butylCellosolve are admixed to obtain a substantially anhydrous soluble oilcomprised of 45 to 75 percent hydrocarbon, 8 to 30 percent surfaceactive agent and 3 to 8 perceint butyl Cellosolve. This anhydroussoluble oil can be used as the miscible displacement agent or Water canbe added to the soluble oil to obtain a water-in-oil microemulsioncontaining up to about 40 percent water.

The soluble oil prepared in the forgoing manner is then injected intothe reservoir through one or more injections Wells in an amountequivalent to 0.01 to 0.15 reservoir pore volume of the reservoir to betreated. Aqueous flooding medium is then injected to displace thesoluble oil toward at least one production well spaced apart in thereservoir, from which fluids are produced in conventional manner. Theaqueous flooding medium can comprise water or brine, and can be mademore viscous by the addition of a thickening agent, such as sugar,dextran, carboxymethyl cellulose, amines, glycerine, guar gum andmixtures of these agents. Also, the aqueous flooding medium can berendered more viscous by the addition of a small amount of awater-soluble polymer, such as 9. polyacrylamide, and particularly apartially hydrolyzed polyacrylamide.

In a preferred method of practicing this invention, thickening agent isadded to only an initial portion of the flood water. Thus, in thispreferred embodiment, 0.01 to 0.15 reservoir pore volume of soluble oilis injected into the reservoir and followed by 0.1 to 0.5 reservoir porevolume of thickened aqueous flooding medium. Thereafter water or brineis injected to drive the previously injected fluids toward at least onespaced production well.

The invention is further described by the following examples which areillustrative of specific modes of practicing the invention and are notintended as limiting the scope of the invention as defined by theappended claims.

EXAMPLE 1 The increased oil recovery obtainable by miscible floodingwith a soluble oil having a composition in accordance with thisinvention is demonstrated by the following laboratory tests. Twosubstantially identical test cores 2 feet long by 1 /2 inches indiameter are prepared by packing Lucite tubes with Nevada 130 sand. Thecores are first saturated with water and then with an Illinois crude oilhaving a gravity of 39 API. Final oil saturation is about 80%.

A miscible displacement fluid is prepared by admix- Severalmicroemulsions are prepared by admixing Illinois crude oil or gasoline,butyl Cellosolve or isopropyl alcohol, and alkyl aryl petroleumsulfonates marketed by the Sonneborn Division of Witco Chemical Company,Inc., under the trademarks Petronate HL and Petronate CR to form ananhydrous soluble oil. Petronate CR is described in Example 1 andPetronate HL is an oil solution containing about 52 percent of alkylaryl sodium sulfonates having a molecular weight in the range of 440 to470 and about 3.5 percent water. The microemulsion is then produced byadding a desired quantity of tap water containing about 700 p.p.m.dissolved salts to the soluble oil.

The cores are flooded with brine until they become watered-out tosimulate a conventional Water flood. Residual oil saturations are 2430percent. Then 0.025 pore volume of a microemulsion is injected into anddriven through the core with 0.40 pore volume of an aqueous 0.2 weightpercent solution of partially hydrolyzed polyacrylamide marketed by theDow Chemical Company under the trademark Pusher 500, and then with anaqueous brine solution. The recovered oil is accumulated and the volumeof oil recovered is measured. The results of these tests are summarizedin Table 1. It is apparent from these data that while butyl Cellosolveeffects some improvement in oil recovery in a soluble oil systemcompounded with gasoline, an unexpectedly large increase in oil recoveryis experienced in a soluble oil system compounded with petroleum crudeoil.

TABLE 1 Microemulsion Composition, Vol. percent Residual Oil Saturationafter Ultimate Oil I-Iydro- Stablnzmg Surfac- Initial Flood, Recovery,Run carbon Agent tant Water Percent Percent 1 Gasoline. 2 Isopropylalcohol. 3 Petronate HL. 4 Butyl Cellosolve. 5 Crude oil. 6 PetronateCR.

ing 72 percent of the Illinois crude, 6.7 percent isopropyl EXAMPLE 3alcohol, and 21.3 percent of a mixed alkyl aryl petroleum monosulfonatemarketed by the Sonneborne Division of Witco Chemical Company, Inc.under the trademark Petronate CR. Petronate CR is an oil solutioncontaining about 62 percent of alkyl aryl sodium sulfonates having amolecular weight in the range of 490 to 510 and about 5 percent water.The first test is conducted by flooding one of the cores with 0.10 porevolume of the anhydrous soluble oil. The soluble oil is driven throughthe core with an aqueous flooding medium thickened by the addition of0.06 weight percent of a partially hydrolyzed polyacrylamide marketed bythe Dow Chemical Company under the trademark Pusher 500. The recoveredoil is accumulated and the voume of oil recovered is measured. Theultimate oil recovery after the injection of 1.3 pore volumes of aqueousflooding medium is 87 percent of the original oil-in-place exclusive ofthe amount of soluble oil injected.

The foregoing test is repeated on the second core using 0.10 pore volumeof a soluble oil in accordance with this invention prepared by admixing72 percent Illinois crude, 21.3 percent Petronate CR and 6.7 percentbutyl Cellosolve. The ultimate oil recovery after the injection of 1.3pore volumes of aqueous flooding medium is 91.8 percent of the originaloil-in-place exclusive of the amount of soluble oil injected.

EXAMPLE 2 A number of substantially identical test cores 6 feet long by1 /2 inches in diameter are prepared by packing Lucite tubes with Nevada130 sand. The cores are first saturated with water and then with anIllinois crude oil having a gravity of 39 API.

A miscible flooding operation is conducted on an oilcontaining reservoirin accordance with the method of this invention. Four injection wellsare arranged in a rectangular pattern around a single centrally locatedproduction well. A miscible displacement fluid comprising amicroemulsion is prepared by admixing 69.2 percent previously recoveredpetroleum crude oil, 6.4 percent butyl Cellosolve, 20.4 percentPetronate CR and 4.0 percent fresh water containing about 900 p.p.m.dissolved salts. The microemulsion is injected into each of theinjection wells at injection rates of 3040 barrels per day until a totalamount of microemulsion equivalent to about 0.05 pore volume isinjected. Thereafter, aqueous flooding medium is injected into thereservoir through each of the injection wells and petroleum and otherproduced fluids are recovered from the central producing well.

Various embodiments and modifications of this invention have beendescribed in the foregoing description and examples, and furthermodification will be apparent to those skilled in the art. Suchmodifications are included within the scope of this invention as definedby the following claims.

Having now described the invention, I claim:

1. In the method of recovering petroleum from a subterranean reservoirin which a miscible displacement fluid miscible with both the connatereservoir oil and with water is injected into the reservoir through aninjection well, and thereafter an aqueous flooding medium is injected todrive the miscible displacement fluid towards a spaced production wellfrom which fluids are recovered, the improvement which comprisesemploying as the miscible displacement fluid a soluble oil comprisingliquid hydrocarbon, a surface active agent and butyl Cellosolve.

2. The method defined in claim 1 wherein said liquid hydrocarbon iscrude petroleum.

3. The method defined in claim 2 wherein said crude petroleum ispreviously recovered from said reservoir.

4. The method defined in claim 2 wherein said miscible displacementfluid also contains an additional quantity of light liquid hydrocarbonto increase the mobility of the miscible displacement fluid to obtain amore favorable mobility ratio between the soluble oil and the followingaqueous flooding medium.

5. The method defined in claim 1 wherein said soluble oil contains waterpresent in the form of a water-in-oil microemulsion.

6. The method defined in claim 1 wherein between about 0.01 to 0.15reservoir pore volumes of said miscible displacement fluid is injectedinto the reservoir.

7. The method defined in claim 1 wherein at least an initial portion ofsaid aqueous medium is increased in viscosity by the addition of athickening agent.

8. The method defined in claim 1 wherein said miscible displacementfluid is comprised of from about 45 to 75 volume percent liquidhydrocarbon, 8 to 30 volume percent surface active agent, and 3 to 8volume percent butyl Cellosolve.

9. The method defined in claim 1 wherein said surface active agent is analkyl aryl sulfonate.

10. The method defined in claim 1 wherein said miscible displacementfluid is comprised of from about 45 to 75 volume percent liquidhydrocarbon, 8 to 30 volume percent alkyl aryl sulfonate, and a minorproportion of butyl Cellosolve.

11. A method for recovering petroleum from a subterranean reservoirpenetrated by an injection well and a production well spaced apart inthe reservoir, which comprises:

injecting 0.01 to 0.15 reservoir pore volume of a soluble oil comprisinga mixture of about to 75 volume percent liquid hydrocarbon, 8 to 30volume percent surface active agent, a minor portion of butylCellosolve, and 0 to 40 percent water, said water being present in theform of a water-in-oil microemulsion;

thereafter injecting an aqueous flooding medium to drive the soluble oiltowards said production well; and

recovering petroleum from said production well.

12. The method defined in claim 11 wherein said liquid hydrocarbon ispetroleum crude oil.

13. The method defined in claim 12 wherein an additional quantity oflight liquid hydrocarbon is added to the soluble oil to increase itsmobility to obtain a more favorable mobility ratio between the solubleoil and the following aqueous flooding medium.

14. The method defined in claim 11 in which an initial portion of theaqueous flooding medium is increased in viscosity by the addition of athickening agent.

15. The method defined in claim 11 wherein said soluble oil containsabout 3 to 8 volume percent butyl Cellosolve.

16. The method defined in claim 11 wherein said surface active agent isalkyl aryl sulfonate.

17. A method for recovering petroleum from a subterranean reservoirpenetrated by an injection well and a production well spaced apart inthe reservoir, which comprises:

injecting 0.01 to 0.15 reservoir pore volume of a soluble oil comprisinga mixture of 45 to volume percent petroleum crude oil, 8 to 30 volumepercent alkyl aryl sulfonate, a minor proportion of butyl Cellosolve,and 0 to 40 percent water, said water being present in the form of aWater-in-oil microemulsion; next injecting 0.1 to 0.5 reservoir porevolume of an aqueous flooding medium thickened by the addition of aminor proportion of a water-soluble polymer;

thereafter injecting a flood water to displace said previously injectedfluids towards said production well; and

recovering petroleum from said production well.

18. The method defined in claim 17 in which an additional quantity oflight liquid hydrocarbon is added to the soluble oil to increase itsmobility to obtain a more favorable mobility ratio between the solubleoil and the following aqueous flooding medium.

19. The method defined in claim 17 wherein said solube oil containsabout 3 to 8 volume percent butyl Cellosolve.

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